Phosphate coating of incandescent lamp



July 15, 1958 H. A. VAN BAKEL ET AL 2,843,504

PHOSPHATE COATING OF INCANDESCENT LAMP Filed Feb. 14, 1955 Envelope Filament INVENTORS HENRICUS ANTONIUS VAN BAKEL THEODORUS ADRIANUS MARIA GAST Q. Uy ym AGENT United States Patent "ice PHOSPHATE CQATING OF INCANDESCENT LAMP Henricus Antonius Van Bake] and Theodcrus Adrianus Maria Gast, Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Compauy, Inc., New York, N. Y., a corporation of Delaware Application February 14, 1955, Serial No. 487,976

3 Claims. (Cl. 1l7 -97) Our invention relates to non-glare envelopes for electric incandescent lamps and methods of preparing the same.

More particularly our invention relates to coated electric incandescent lamps which allow the maximum amount of light to pass through the envelope while preventing the filament from showing through.

It is a principal object of our invention to provide an electric incandescent lamp allowing the maximum amount of light to pass through the envelope while preventing the filament from showing through.

It is another object of our invention to provide a simpler method of making non-glare electric incandescent lamps.

It is a further object of our invention to provide a coated envelope for an electric incandescent lamp having a high light-transmissibility.

In accordance with our invention, we provide on the internal surface of a light transparent envelope adapted to house an incandescent filament a coating of a water insoluble alkaline-earth phosphate preferably having an apatite structure. Such coatings, we have found are easy to apply, transmit over 95% of the light generated by the filament, whilst preventing the filament from shining through.

The coating material in this invention may be applied in any known manner. For example a suspension of the phosphate may be applied to the surface by spraying, or by sliding the suspension on the surface the excess of the suspension being allowed to flow away and the residual layer dried.

Excellent results are produced when the suspension of the water-insoluble alkaline-earth phosphate contains in addition at least 1.5% of phosphoric acid (based on the phosphate). Other acids which liberate the required amount of phosphoric acid from the phosphate, such as for example, hydrochloric acid may be used. The suspending medium used is a water-mixable volatile organic liquid to which water (preferably about 3% based on the phosphate) is added. As the volatile organic liquid we may use methanol, ethanol, acetone or methyl ethyl ketone.

This suspension is applied to the bulb surface and is dried by a flow of air. The drying air may be heated if desired. After the layer is dried it is heated above approximately 200 C. This process produces a layer that adheres very well to the bulb surface. In those areas at which parts are to be sealed to the bulb surface it is necessary that the layer be removed prior to the heating above 200 C.

The phosphate may be used in the form of orthophos- Patented July 15, 1958 phates, metaphosphates or pyrophosphates, for example Ca (PO Mg P O- and Ba(PO However, best results are obtained when the phosphate used has the apatite structure. Suitable apatites are for example halogen apatites such as fluoro-apatite having the formula 3Ca (PO ).CaF or a hydroxy-apatite having the formula 3Ca (PO,).Ca(OH) Example 3750 gms. of one of the above phosphates were placed together with 135 cc. of water, 155 cc. of phosphoric acid (specific gravity 1.75) and 3.75 liters of methanol in a porcelain ballmill having a capacity of liters and the mixture ground for 4 to 24 hours. The suspension thus obtained containing particles less than 31.4. was diluted with 10.4 liters of ethanol.

This suspension was sprayed on the inside of a bulb which had not been etched. After the excess of suspension was allowed to leak out, the layer was dried by blowing in hot air. The layer was then removed at the sealing area with the use of a rotating brush and finally heated at 500 C. for 1 minute. The bulb was finished in the usual manner and used in the manufacture of incandescent lamps.

Such a process produces a uniform light-diffusing layer adhering very well to the bulb surface and] thick enough to prevent the filament from shining through. This bulb also passes through more than of the light that a similar but uncoated bulb would emit. When the phosphates used have the apatite structure a light output of as much as 97% of the uncoated bulb is achieved.

While we have described our invention with specific examples and applications, other modifications thereof will be apparent to those skilled in the art without departing from the scope of the invention as defined in the appended claims:

What is claimed is:

1. A process of coating the inner side of an envelope of an incandescent lamp with a light diffusing layer which comprises the steps, preparing a stable suspension of a water-insoluble alkaline earth phosphate in a mixture of water, a water-miscible volatile organic liquid and at least 1.5% based on the weight of phosphate of an acid selected from the group consisting of phosphoric acid and acids that liberate phosphoric acid from the phosphate, applying a layer of the suspension to the inner surface of the envelope, removing excess suspension from the envelope, drying the residual layer and finally heating the dried layer to a temperature of at least 200 C.

2. The process of claim 1 in which the alkaline earth phosphate has the apatite structure.

3. The process of claim 1 in which the apatite is selected from the group consisting of calcium fluoro-apatite and calcium hydroxy-apatite.

References Cited in the file of this patent UNITED STATES PATENTS 2,324,079 Greger July 13, 1943 2,684,306 Brewer July 20, 1954 2,686,734 Sadowsky Aug. 17, 1954 2,691,601 Butler Oct. 12, 1954 2,704,726 Markoski Mar. 22, 1955 2,706,691 Schaefer Apr. 19, 1955 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,823,594 July 1.5, 1958 Henrieue Antonius Van Bakel et all,

hat error appears in the above numbered It is hereby certified t the said Letters Patent ehould read patent requiring correction and that as corrected belowo cation, between lines 9 and 10,

In the needing to the printed epeeiii herlande February 26, 195A insert M Claims priority, application Net Signed and sealed this 4th day of November 1958.

(SEAL) Attest:

KARL Ho AXLINE ROBERT C. WATSON Attesting Officer Conmissioner of Patents 

1. A PROCESS OF COATING THE INNER SIDE OF AN ENVELOPE OF AN INCANDESCENT LAMP WITH A LIGHT DIFFUSING LAYER WHICH COMPRISES THE STEPS, PREPARING A STABLE SUSPENSION OF A WATER-INSOLUBLE ALKALINE EARTH PHOSPHATE IN A MIXTURE OF WATER, A WATER-MISCIBLE VOLATILE ORGANIC LIQUID AND AT LEAST 1.5% BASED ON THE WEIGHT OF PHOSPHATE OF AN ACID SELECTED FROM THE GROUP CONSISTING OF PHOSPHORIC ACID AND ACIDS THAT LIBERATE PHOSPHORIC ACID FROM THE PHOSPHATE, APPLYING A LAYER OF THE SUSPENSION TO THE INNER SURFACE OF THE ENVELOPE, REMOVING EXCESS SUSPENSION FROM THE ENVELOPE, DRYING THE RESIDUAL LAYER AND FINALLY HEATING THE DRIED LAYER TO A TEMPERATURE OF AT LEAST 200*C. 